Omaha: Dana Vollmer ended 12 years of frustration on Tuesday when she won the women's 100 meters butterfly at the U.S. Olympic swimming trials to book her place on the team for London.

Although Vollmer won a relay gold medal at the 2004 Olympics in Athens, the 24-year-old had never qualified in an individual event despite three previous attempts.

In 2000, she was just a bright-eyed 12-year-old who was not expected to qualify. Even in 2004 she was a surprise qualifier, earmarked as a future champion.

In 2008, however, the combination of a mystery illness and the weight of expectation got the better of her and she failed to qualify at all.

Now married and with her illness behind, she made amends on Tuesday, thrashing through the water like a woman possessed to win in 56.50 seconds, less than half a second outside the world record set by Sweden's Sarah Sjoestroem at the 2009 world championships in Rome.

"I think the relief comes from ... just not wanting to mess up," she said.

"(That) was kind of where my nerves come from, not twitching on the blocks like I did in 2008.

"As soon as I was in the water I was excited and felt more in control of that race than I think any of my (previous) 100 fly swims."

Claire Donahue, swimming from the outside lane, sliced a quarter of a second off her best time to finish second in 57.57 and qualify for her first Olympics, but all the plaudits went to Vollmer.

In 2003, she underwent heart surgery to correct a condition which produced a faster than normal pulse but it was an allergy to eggs that held her back for many more years.

When it was finally diagnosed, after missing out on the Beijing Olympic team, she was put on a new gluten-free diet.

Her results in the pool quickly started to improve and in 2011 she won her first individual world title at Shanghai, and now goes to London as one of the favorites to win gold.

"It's just neat to reflect on where I've come since 2008," she said,

"I am in such a different place now, and when I think about myself and how I feel in the water, I was confident in what I could do. I just had to keep my mind off of how I felt in 2008 and just focus on where I am now."